Niobium and chromium low alloy carbon steel for high wear resistant automotive chain link plates

ABSTRACT

Niobium chromium low allow carbon steel for automotive chain link plates has improved wear resistance. In one preferred embodiment, the steel composition includes niobium, chromium, carbon, iron, and any impurities. One preferred composition including these components includes, by weight percentage, approximately 0.25% to 0.75% carbon, approximately 0.20% to 2.0% chromium, approximately 0.26% to 1.5% niobium, and the remaining component of the composition is iron. Trace amounts of impurities may also be present. In another embodiment, a steel composition includes, by weight percentage, approximately 0.25% to 0.75% carbon, approximately 0.2% to 1.0% manganese, approximately 0.05% to 0.60% silicon, approximately 0.26% to 1.5% niobium, approximately 0.20% to 2.0% chromium, up to approximately 0.30% aluminum, up to approximately 0.03% phosphorus, up to approximately 0.03% sulfur, and a remainder of the composition being iron and any other impurities.

BACKGROUND OF THE INVENTION Field of the Invention

The invention pertains to the field of steel compositions. Moreparticularly, the invention pertains to steel compositions forautomotive chain link plates.

Description of Related Art

A lot of effort has been put into developing wear resistant chains. Onedesire is to reduce wear and frictional losses for the next generationof engine timing chains to be used in gasoline direct injection (DI)engines and diesel engines. Current production chains in these types ofengines have high wear or chain elongations and friction losses, whichresult in poor engine fuel efficiency and high emission, or even enginefailure due to the malfunction of elongated chains which can cause toothjump that leads to vehicle safety concerns. The prior art has mainlyseen chain pin developments such as vanadium carbide (VC) pins or VCcoated pins and stainless steel nitrided (SSN) pin technologies. Thereis a need in the art for more resistant timing chains for gasolinedirect injection and diesel engines.

SUMMARY OF THE INVENTION

An optimum steel composition for automotive chain link plates hasimproved wear resistance. The composition is preferably low alloy carbonsteel with niobium and chromium.

In one embodiment, a steel composition includes, by weight percentage,approximately 0.25-0.75% carbon, approximately 0.20-2.0% chromium,approximately 0.26-1.5% niobium, and the remainder of the composition isiron and any impurities. This composition may also optionally includeone or more of the following: approximately 0.2 to 1.0% manganese,approximately 0.05 to 0.60% silicon, up to approximately 0.30% aluminum,up to approximately 0.03% phosphorus, or up to approximately 0.03%sulfur.

In another embodiment, a steel composition includes, by weightpercentage, approximately 0.25 to 0.75% carbon, approximately 0.2 to1.0% manganese, approximately 0.05 to 0.60% silicon, approximately0.26-1.5% niobium, approximately 0.20 to 2.0% chromium, up toapproximately 0.30% aluminum, up to approximately 0.03% phosphorus, upto approximately 0.03% sulfur, and a remainder of the composition beingiron and any other impurities.

The compositions described herein are preferably used for automotivechain link plates. The chain links are preferably heat treated to ahardness in the range of HRc 50 to 60, either by oil quenching andtempering or salt bath austempring and/or martempering preferably bysalt bath austempering and/or martempering.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of a chain link/chain link plate that could bemade using the compositions described herein.

FIG. 2 shows an example of a silent chain including chain links thatcould be made using the compositions described herein.

FIG. 3A shows a top view of an example of a roller chain that could bemade using the compositions described herein.

FIG. 3B shows a side view of the roller chain of FIG. 3A.

FIG. 3C shows a section of the roller chain along line 3C-3C of FIG. 3A.

FIG. 4A shows a top view of an example of a bushing chain that could bemade using the compositions described herein.

FIG. 4B shows a side view of the bushing chain of FIG. 4A.

FIG. 4C shows a section of the bushing chain along line 4C-4C of FIG.4A.

DETAILED DESCRIPTION OF THE INVENTION

An optimum steel composition for automotive chain link plates hasimproved wear resistance. The composition is preferably Nb Cr low alloycarbon steel. The chain link plates made with the compositions arepreferably used in silent chains, roller chains or bushing chains.

In one preferred embodiment, the steel composition includes niobium,chromium, carbon, iron, and any impurities. One preferred compositionincluding these components includes, by weight percentage, approximately0.25%-0.75% carbon, approximately 0.20%-2.0% chromium, approximately0.26%-1.5% niobium, and the remaining component of the composition isiron. The amount of iron in the composition is the remainder of theweight percentage of the composition not made of other components in thecomposition. Trace amounts of impurities may also be present.

The composition may also include one or more of the following additionalcomponents (by weight percentage): approximately 0.2%-2.0% manganese,approximately 0.05%-0.60% silicon, up to approximately 0.30% aluminum,up to approximately 0.03% phosphorus, and up to approximately 0.03%sulfur. The amount of iron in the composition is the remainder of theweight percentage of the composition not made of other components in thecomposition.

The chain link plates made using this steel composition are preferablyheat treated to a hardness in the range of HRc 50 to 60. In someembodiments, heat treatment occurs either by oil quenching and temperingor salt bath austempring and/or martempering preferably by salt bathaustempering and/or martempering. In some embodiments, the hardness isin the range of HRc 52 to 58.

In one preferred embodiment, the composition includes the followingpercentages (wt %) of materials:

C Mn Si Nb Cr Al P S 0.25-0.75% 0.2-1.0% 0.05-0.60% 0.26-1.5% 0.20-2.0%0.30% 0.03% 0.03% max max max

The percentages of aluminum, phosphorus, and sulfur are preferablymaximum amounts of each of these materials. Phosphorus and sulfur areimpurities in steel and are preferred to be zero or as close to zero aspossible. Aluminum is also an impurity, and should be kept as low aspossible except in special applications. The remainder of the steelcomposition is composed of iron and any other impurities.

Steel compositions always have impurities and inclusions including, butnot limited to, Sulfides (MnS), Alumina, and Silicate. There areindustry standards to evaluate the inclusions. One of the most common isASTM E45. This standard or other industry standards are used to controlthe amount of the impurities to an acceptable level.

The amount of iron in the composition is the remainder of the weightpercentage of the composition not made of other components in thecomposition. The chain link plates of this steel composition are heattreated to a hardness of HRc 50-60. In some preferred embodiments, heattreatment uses either oil quenching and tempering or salt bathaustempering and/or martempering by salt bath. In some embodiments, thehardness is in the range of HRc 52 to 58.

The steel composition for the chain links described herein fill the gapto further improve the wear resistance of the chains. The compositionincludes carbon, niobium, chromium, and iron. The steel of thecomposition preferably has a range of carbon from 0.25% to 0.75 wt %,which makes the steel hardenable after heat treatment. In some preferredembodiments, the carbon weight percentage ranges from 0.5-0.6%.

The composition also preferably includes a range of chromium from0.2%-2.0 wt %, which improves the hardenability of the steel and makesthe steel suitable for either oil quenching and tempering oraustempering and martempering as hardening options. In some preferredembodiments, the chromium weight percentage ranges from 0.4%-0.6%.

The composition also preferably includes a weight percentage of niobiumin the range of 0.26% to 1.5 wt %. In some preferred embodiments, theniobium content, by weight percentage, is between approximately 0.26%and 0.8%. In other embodiments, the niobium weight percentage in thecomposition is between 0.5% and 1.5%. In other embodiments, the niobiumcontent, by weight percentage, is between 0.5% and 0.8%.

The niobium content in the steel composition not only inhibits the graingrowth of the steel and results in a fine grained high strength steel,the niobium also forms nanoscale Niobium Carbide particles after heattreatment. Increased Niobium content results in more Niobium Carbideprecipitation, with proper heat treatment. These particles areparticularly prevalent if an austempering or martempering process isused for heat treatment, because of the limited solubility of niobium insteel (1.5% max in austerilized iron) and the reduced solubility withreductions of temperature during heat treatment. When the carbidesdistribute uniformly in the steel matrix in sub-micrometer and nanometerscale particles, the wear resistance of the steel increases greatlywithout negative impact on its fatigue properties, which are highlydesired for the silent chain links. As a result, the wear resistance ofthe link plates are significantly improved.

The composition may also include one or more of the following additionalcomponents (by weight percentage): approximately 0.2%-2.0% manganese,approximately 0.05%-0.60% silicon, up to approximately 0.30% aluminum,up to approximately 0.03% phosphorus, and up to approximately 0.03%sulfur. The amount of iron in the composition is the remainder of theweight percentage of the composition not made of other components in thecomposition.

In one preferred embodiment, the composition includes the followingpercentages (wt %) of materials:

C Mn Si Nb Cr Al P S 0.25-0.75% 0.2-1.0% 0.05-0.60% 0.26-1.5% 0.20-2.0%0.30% 0.03% 0.03% max max max

In some of these embodiments, the carbon weight percentage ranges from0.5%-0.6%, the chromium weight percentage ranges from 0.4%-0.6%, and/orthe niobium content, by weight percentage, ranges from 0.26% and 0.8%.In other embodiments, the niobium content, by weight percentage, isgreater than 0.5%. In other embodiments, the niobium content, by weightpercentage, is between 0.5% and 0.8%. The amount of iron in thecomposition is the remainder of the weight percentage of the compositionnot made of other components in the composition.

FIG. 1 shows an example of a chain link plate 1 that can be made usingthe compositions described herein. FIG. 2 shows an example of a silentchain 10 including chain links 1 made using the compositions describedherein. The chain includes guide or outside links A and inside links B,as well as pins 2. Any component of the silent chain 10 may be made ofthe compositions described herein.

FIGS. 3A-3C show an example of a roller chain 20 with bushings 35 thatcan be made using the compositions described herein. The roller chain 20includes guide links 30, bushing links 31, rollers 32, pins, 33, 34 andbushings 35. Any component of the roller chain 20 may be made of thecompositions described herein.

FIGS. 4A-4C show an example of a bushing chain 25 with bushings 45 thatcan be made using the compositions described herein. The bushing chain25 includes guide links 40, bushing links 41, pins 43, and bushings 45.Any component of the bushing chain 25 may be made of the compositionsdescribed herein.

In preferred embodiments, the compositions described herein are used tomake silent chain inside links B, which articulate with the pins 2 andhave issues with wear. While it is not necessary to also use the steelcompositions described herein for the guide links A, the compositionsmay also be used for the guide links A.

In other embodiments, the compositions described herein are used to makebushings 35, 45 in a roller chain 20 or a bushing chain 25. Thecompositions may also or alternatively be used to make the links 30, 31,40, 41, the rollers 32, and/or other components of these types ofchains.

The chain link plates made using the steel compositions described hereinare preferably heat treated to a hardness in the range of HRc 50 to 60.In some embodiments, the composition is heat treated either by oilquenching and tempering or salt bath austempring and/or martemperingpreferably by salt bath austempering and/or martempering. In someembodiments, the hardness of the chain link plates is in the range ofHRc 52 to 58.

In some embodiments, chain link plates made with the compositiondescribed herein are used in combination with advanced pin technologiesincluding, but not limited to, VC pins or SSN pins.

In some embodiments, the composition does not include tungsten (W). Insome embodiments, the composition does not include any molybdenum (Mo).In some embodiments, the composition does not include titanium (Ti),Nickel (Ni), and/or boron (B).

The chain link plate compositions described herein create a more wearresistant chain. Due to the improved wear resistance of the steelcompositions described herein, it is unnecessary to coat the chain linkplates made with the compositions. This eliminates both the cost andtime associated with expensive coating processes.

Accordingly, it is to be understood that the embodiments of theinvention herein described are merely illustrative of the application ofthe principles of the invention. Reference herein to details of theillustrated embodiments is not intended to limit the scope of theclaims, which themselves recite those features regarded as essential tothe invention.

1.-10. (canceled)
 11. A chain link comprising a steel compositioncomprising, by weight percentage, approximately 0.25% to 0.75% carbon,approximately 0.26% to 1.5% niobium, approximately 0.20% to 2.0%chromium, iron and any impurities.
 12. The chain link of claim 11,wherein the chain link has a hardness of HRc 50 to
 60. 13. The chainlink of claim 12, wherein the chain link has a hardness of HRc 52 to 58.14. The chain link of claim 11, wherein the weight percentage of carbonin the composition ranges from approximately 0.5% to 0.6%.
 15. The chainlink of claim 11, wherein the weight percentage of chromium in thecomposition ranges from approximately 0.4% to 0.6%.
 16. The chain linkof claim 11, wherein the weight percentage of niobium in the compositionis greater than 0.5%.
 17. The chain link of claim 11, wherein the weightpercentage of niobium in the composition ranges from approximately 0.26%to 0.8%.
 18. The chain link of claim 11, wherein the composition furthercomprises, by weight percentage, approximately 0.2% to 1.0% manganese.19. The chain link of claim 11, wherein the composition furthercomprises, by weight percentage, approximately 0.05% to 0.60% silicon.20. The chain link of claim 11, wherein the composition furthercomprises at least one impurity, by weight percentage, selected from thegroup consisting of: a) up to approximately 0.3% aluminum; b) up toapproximately 0.03% phosphorus; c) up to approximately 0.03% sulfur; andd) any combination of up to approximately 0.3% aluminum, up toapproximately 0.03% phosphorus and up to approximately 0.03% sulfur. 21.The chain link of claim 11, wherein the composition further comprisesapproximately 0.2% to 1.0% manganese and approximately 0.05% to 0.60%silicon. 22.-36. (canceled)
 37. A chain link comprising a compositioncomprising, by weight percentage, approximately 0.25% to 0.75% carbon,approximately 0.2% to 1.0% manganese, approximately 0.05% to 0.60%silicon, approximately 0.26% to 1.5% niobium, approximately 0.20% to2.0% chromium, up to approximately 0.30% aluminum, up to approximately0.03% phosphorus, up to approximately 0.03% sulfur, and a remainder ofthe composition being iron and any other impurities.
 38. The chain linkof claim 37, wherein the chain link has a hardness of HRc 50 to
 60. 39.The chain link of claim 38, wherein the chain link has a hardness of HRc52 to
 58. 40. A chain that includes a plurality of links, each linkcomprising a steel composition comprising, by weight percentage,approximately 0.25% to 0.75% carbon, approximately 0.2% to 1.0%manganese, approximately 0.05% to 0.60% silicon, approximately 0.26% to1.5% niobium, approximately 0.20% to 2.0% chromium, up to approximately0.30% aluminum, up to approximately 0.03% phosphorus, up toapproximately 0.03% sulfur, and a remainder of the composition beingiron and any other impurities.
 41. The chain of claim 40, wherein thelinks have a hardness of HRc 50 to
 60. 42. The chain of claim 41,wherein the links have a hardness of HRc 52 to
 58. 43. A method ofproducing a chain link, comprising the step of heat treating a steelcomposition comprising by weight percentage, approximately 0.25% to0.75% carbon, approximately 0.2% to 1.0% manganese, approximately 0.05to 0.60% silicon, approximately 0.26% to 1.5% niobium, approximately0.20 to 2.0% chromium, up to approximately 0.30% aluminum, up toapproximately 0.03% phosphorus, up to approximately 0.03% sulfur, and aremainder of the composition being iron and any other impurities, to ahardness of HRc 50 to
 60. 44. The method of claim 43, wherein the heattreating step uses a method selected from the group consisting of oilquenching and tempering, salt bath austempering, and salt bathmartempering.